Electrical energy storage devices, particularly batteries, which employ fibrous carbon or graphite electrodes and which operate in a nonaqueous electrolyte at ambient temperature are known from U.S. Pat. No. 4,865,931, issued Sep. 12, 1989 to F. P. McCullough et al, the subject matter of which is, in its entirety, incorporated herein by reference. The patent generally discloses a secondary battery comprising a housing having at least one cell positioned in the housing, each cell comprising a pair of electrodes made of a multiplicity of electrically conductive carbon fibers, a foraminous electrode separator for electrically insulating the electrodes from contact with each other, and an electrolyte comprising an ionizable salt in a nonaqueous fluid in each cell.
A similar electrical storage device is disclosed in U.S. Pat. No. 4,830,938 to F. P. McCullough et al, issued May 16, 1989, the subject matter of which is incorporated herein, in its entirety, by reference. This patent discloses a fibrous carbonaceous electrode which is characterized as having a Young's modulus of greater than 1 MM psi (6.9 GPa) and a surface area with respect to the fibrous material of at least 0.1 m.sup.2 /g, most preferably less than 5 m.sup.2 /g. The patent additionally discloses a shared bipolar carbonaceous electrode which is capable of carrying a current from one cell to an adjacent cell without a current collector frame associated therewith and, when employed as the electrode in a series of adjacent cells of a battery, having a pair of terminal electrodes each provided with a collector frame at the terminal cells of the battery. The useable capacities of the circular cross-section fiber electrodes of these batteries was less than 1 Li per 6 carbons on the anode (negative electrode) side and less than 1 anion per 12 carbons on the cathode (positive electrode) side.
The physical shape of nongraphitic and electrically nonconductive polymeric fibers is described in Modem Textiles, second edition, 1982, by D. S. Lyle, John Wiley & Sons. In the chapter entitled "Fiber Properties", pp. 41 to 63, various natural and polymeric fibers are described having different surface contours, i.e. smooth, rough, serrated, etc. which are said to influence cohesiveness, resiliency, loft, and thickness. Polymeric fibers having various cross-sectional shapes are described in Table 2-9 on pages 52 and 53 and include tubular, triangular, irregular striated, oval, etc.
It is now well understood in this art that the carbon electrodes for secondary electrical energy storage devices require a special type of carbon or graphite, particularly when used as the positive electrode in nonaqueous battery systems due to destructive intercalation of large anions from the electrolyte entering between the planar graphite layers. These large anions which enter between the planar graphite layers (usually referred to as "d-spacing" in the art) cause spalling or flaking of the carbon or graphite layers and can thus bring about a rapid degradation of the electrode when subjected to repeated electrical charging and discharging cycles. Accordingly, destructive intercalation of large anions between the carbon or graphite layers of an electrode and electrolyte instability becomes a particular problem with rechargeable batteries, that operate with a nonaqueous electrolyte and that have a cell voltage of greater than 2.5 volts. Such batteries require exacting standards during their manufacture and operation to prevent the introduction of gaseous water or water vapor into the batteries since the introduction of only minute quantities of water into a battery, i.e. in the range of parts per million (ppm), results in the electrolysis of the water molecule. Electrolysis of water molecules can take place during electrical charging of the battery at a potential of greater than 2.5 V, during storage in the charged state, or during discharge of the battery, forming O, OH.sup.- and H.sup.+ ions with the OH.sup.- ions migrating to the positively charged cathode where electrolysis to O and O.sub.2 takes place. Species such as OH.sup.- and H.sup.+ cause a breakdown of such commonly used nonaqueous electrolyte materials such as propylene carbonate through catalysis, while highly reactive O and O.sub.2 destroy the surface of the carbon or graphite electrode due to destructive intercalation. McCullough et al report that their battery is capable of operating with a water content of up to 300 ppm but that it will have a somewhat reduced cycle life. McCullough et al also report that, if the water content should become onerous, the battery can be disassembled, dried and reassembled in a dried state without substantial damage to its continued operation.